
theorem
  for S1, S2 being Graph-membered set st S1, S2 are_Disomorphic
  holds S1, S2 are_isomorphic
proof
  let S1, S2 be Graph-membered set;
  assume S1, S2 are_Disomorphic;
  then consider f being one-to-one Function such that
    A1: dom f = S1 & rng f = S2 and
    A2: for G being _Graph st G in S1 holds f.G is G-Disomorphic _Graph;
  take f;
  thus thesis by A1, A2;
end;
